The present invention relates to a safety brake, with a retardation-dependent braking force, for a load receiving means of an elevator, which brake is triggered by an elevator speed limiter in the case of excess speed of the load receiving means, wherein at least one brake wedge penetrates into a tapering gap between a resiliently supported pressure body of the safety brake and a guide rail of the load receiving means and thereby generates a braking force and wherein the magnitude of this braking force is dependent on the retardation occurring at the load receiving means.
In the case of usual safety brakes a safety brake base body engages around the guide web of a guide rail of the load receiving means and includes at least one pressure body, which on the one hand forms, together with the guide web, a gap tapering in opposite direction to the direction of travel of the load receiving means and on the other hand is movable, counter to a spring element, perpendicularly to the guide web. In the case of excess speed of the load receiving means, a speed limiter mechanism displaces a brake wedge into the tapering gap between the pressure body and the guide web moving relative thereto, whereupon the brake wedge is drawn into the tapering gap by friction at the guide web up to an abutment at the base body and then slides along the guide web until standstill of the load receiving means. The pressure body is forced against the spring element by the wedge effect. The spring force resulting therefrom acts by way of the pressure body on the brake wedge and determines the perpendicular force arising between the brake wedge and the guide web and thus the arising frictional force acting as braking force at the load receiving means.
Such safety brakes have the disadvantage that the perpendicular force acting on the brake wedge is always of the same size independently of different useful loads in the load receiving means and other influences, such as, for example, the state and contamination of the brake surfaces, the instantaneous speed and the ambient temperature. This has the consequence that, in the case of braking, significantly different retardation values occur at the load receiving means. Since, for reasons for safety, a certain minimum retardation must be guaranteed, retardation values beyond the permissible limit value often result in the case of a minimum useful load.
There is known from the German patent document DE 39 34 492 a safety brake, which is fastened to load receiving means of an elevator, with a safety brake body constructed as a clasp with non-crossing clasp arms, in which on one side of the clasp joint the clasp arms embrace the guide web of a guide rail. One of these clasp arms at the guide rail side has a fixed friction element and the other is formed as a pressure body which, together with the guide web, forms a gap tapering in the opposite direction to the direction of travel of the load receiving means. A brake wedge is mounted between the pressure body and the guide web and does not contact the guide web in normal operation. On the other side of the clasp joint a biased spring element produces a spreading force on the clasp arms, which in normal operation act on an abutment limiting the opening width of the clasp arms.
In the case of excess speed of the load receiving means a speed limiter mechanism lifts the brake wedge, whereby this comes into contact with the guide web moving relative to the safety brake and is drawn by the web, through friction, into the tapering gap up to an abutment. The consequentially arising clamping force spreads the clasp arms at the side of the guide rail, whereby, on the other side of the clasp, the biased spring element is pressed. The biasing force of this spring element now presses the friction element by way of the clasp arms on the one hand and the pressure body and brake wedge on the other hand against the guide web, whereby a braking forces arises at the load receiving means.
In order to adapt the braking force, which is produced by this safety brake, to the respective conditions influencing the braking process, i.e. to always be able to achieve the same retardation at the load receiving means, the safety brake constructed as a clasp has at its clasp arms at the spring element side an electromagnet system which, in the case of a safety braking, counteracts the spring force of the spring element and thereby the perpendicular force acting on the brake wedge and thus reduces the braking force. The force effect of the lifting magnet system or the size of the braking force reduction is so regulated by a current regulator in dependence on the signal of a retardation measuring sensor that the load receiving means is always braked with the same retardation.
Such a safety brake has the disadvantage that it requires a large installation area, especially because the electromagnet system has to act on relatively long clasp arms in order to be able to influence the large braking perpendicular force in a sufficient range. Moreover, it requires a complicated electronic regulating device that imposes substantial demands with respect to functional reliability. In addition, an emergency current supply is necessary so that this remains functionally capable even in the event of a power failure.
The present invention has the object of proposing a safety brake which always brakes the load receiving means with the same retardation independently of different useful loads in the load receiving means and of other influences, such as, for example, the state and the contamination of the brake surfaces, the instantaneous speed and the ambient temperature.
The safety brake according to the present invention has significant advantages. It is based on safety brake technology known for a long time and needs little more installation space than a conventional construction. It does not require any electronic regulating device, which has to satisfy high demands in terms of technical reliability, and in the case of power failure is still functionally capable with only an emergency current supply. It is simple to understand, install and adjust. Vibration problems in consequence of regulating fluctuations cannot arise. A large number of existing conventional safety brakes can be retrofitted with components according to the present invention.
In an advantageous development of the device according to the present invention the speed at which the brake wedge penetrates into the tapering gap between pressure body and guide rail is limited during the entire penetration travel by a speed limiting device. It is thereby achieved that, in the case of safety braking, an abrupt build-up of the overall braking force and thus a correspondingly strong jolt on the load receiving means are avoided.
The stroke limiting device, which limits the penetration stroke of the brake wedge in dependence on the retardation of the load receiving means, preferably consists of a hydraulic system. Large forces, such as can occur in this connection, can be managed by hydraulic means on a smallest possible installation area.
In expedient manner the speed limiting device, which limits the penetration speed of the brake wedge, is also realized by hydraulic means. Such a solution is functionally reliable and adjustable in simple manner.
In a particularly simple embodiment of the invention the stroke limiting device for the brake wedge consists of a hydraulic cylinder with a piston rod, a hydraulic fluid container and a control valve arranged therebetween, wherein a retardation sensor so influences the control valve that this blocks the movement of the hydraulic cylinder and thus the further penetration of the brake wedge as soon as and for as long as the retardation of the load receiving means exceeds a specific value.
A further advantageous development of the invention consists in that the retardation sensor is a weight body which is movably connected with the load receiving means and the inertial force, which arises through the retardation of the load receiving means, of which influences the control valve by way of a lever system. The inertial force in that case usual acts against a spring, the spring constant of which is determined in dependence on the inertial force of the control valve stroke.
The weight body of the retardation sensor is preferably displaceably arranged on a first arm of a two-arm lever, so that there can be set at which retardation of the load receiving means the inertial force thereof has the effect of reversing the second lever arm of the control valve against the spring effect.
It is expedient to realize the speed limiting device for limitation of the penetration speed of the brake wedge in such a manner that an adjustable hydraulic flow valve limits the flow of the hydraulic fluid which flows from the hydraulic cylinder, which limits the penetration depth of the brake wedge, by way of the control valve to the hydraulic fluid container.
In a preferred embodiment the flow valve limiting the penetration speed of the brake wedge is constructed as an orifice valve or as an adjustable flow regulating valve. Orifice valves have a throttle effect virtually independent of temperature and viscosity of the hydraulic fluid. Flow regulating valves cause a constant throughflow independently of the prevailing pressure of the hydraulic fluid and thus guarantee a constant penetration speed of the brake wedge.
In a further embodiment of the invention the retardation sensor consists of a retardation sensor which is mounted at the load receiving means and in which, for example, a strain gauge force sensor detects the inertial force, which results from the retardation of the load receiving means, of a measuring body and influences an amplifier circuit which electromagnetically actuates the control valve.
A further advantageous development of the invention consists in that the hydraulic fluid container is constructed as a pressure storage device. In this manner the entire stroke and speed limiting system for the brake wedge is a closed hydraulic system standing under low excess pressure. Air inclusions, which are caused by vibrations, in the hydraulic fluid and the contamination thereof are thus excluded, which ensures a highest functional reliability of the system. Moreover, automatic resetting of the hydraulic cylinder after an instance of braking is effected by the mentioned excess pressure instead of by a compression spring.
In a preferred embodiment of the safety brake this comprises a single hydraulic block which contains all connecting ducts of the hydraulic system, wherein all other components of the hydraulic system are either integrated in this block or fastened thereto.